If 8 February 2005 was a Tuesday, what was the day of the week on 8 February 2004?

Introduction / Context:
This question takes you one year back from a known weekday. You are given that 8 February 2005 was a Tuesday and asked to find the weekday on 8 February 2004. Since 2004 is a leap year, you must pay attention to whether the interval includes 29 February and how that affects the number of odd days between the two dates.

Given Data / Assumptions:

• 8 February 2005 was a Tuesday.
• We must find the weekday on 8 February 2004.
• Year 2004 is a leap year.
• 8 February is before 29 February in a leap year.

Concept / Approach:
Between identical calendar dates in consecutive years, the weekday shift depends on both the total days between them and whether the leap day lies in the interval. From 8 February 2004 to 8 February 2005 we cross 29 February 2004, so we must treat the interval as containing a leap day. This leads to 366 days and 2 odd days between the dates.

Step-by-Step Solution:
Step 1: Recognise that 2004 is a leap year, so it has 366 days. Step 2: From 8 February 2004 to 8 February 2005, the interval includes 29 February 2004 because that date lies between them. Step 3: Therefore, the number of days between 8 February 2004 and 8 February 2005 is 366. Step 4: 366 days correspond to 2 odd days because 366 = 7 * 52 + 2. Step 5: This means that moving forward from 8 February 2004 to 8 February 2005 advances the weekday by two days. Step 6: We are told that 8 February 2005 is Tuesday, so 8 February 2004 must be two days earlier: one day earlier is Monday, two days earlier is Sunday. Hence the weekday on 8 February 2004 is Sunday.

Verification / Alternative check:
You can verify by moving forward from the assumed day for 2004. If 8 February 2004 is Sunday, then adding two odd days for the interval gives Tuesday for 8 February 2005, which matches the given information exactly. This confirms that Sunday is the only consistent answer.

Why Other Options Are Wrong:
Tuesday: This would imply zero odd days between the two dates, which is not true for an interval including a leap day.

Monday: This would correspond to only one odd day difference, but the interval has two odd days.

Wednesday: This would suggest that the weekday moved forward instead of backward when we go from 2005 to 2004.

Common Pitfalls:
A typical mistake is to treat every year gap as 365 days and assume only one odd day, ignoring the presence of a leap day. Another common confusion is not checking whether 29 February lies between the two dates or not. Always identify whether the leap day is included in the interval and adjust the odd days accordingly.

Final Answer:
Thus, the day of the week on 8 February 2004 was Sunday.